From 794f158029ef32abd7219b0da9b642394ed88ad7 Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 03:07:44 +0100
Subject: [PATCH 01/14] fix(router-core): avoid infinite type recursion in
 serializer

---
 .../src/ssr/serializer/transformer.ts         | 53 ++++++++++++-------
 .../tests/serializer-recursion.test-d.ts      | 15 ++++++
 2 files changed, 50 insertions(+), 18 deletions(-)
 create mode 100644 packages/router-core/tests/serializer-recursion.test-d.ts

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index 3974a25bf8..206fae1cec 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -32,19 +32,21 @@ export interface CreateSerializationAdapterOptions<TInput, TOutput> {
 
 export type ValidateSerializable<T, TSerializable> = T extends TSerializable
   ? T
-  : T extends (...args: Array<any>) => any
-    ? 'Function is not serializable'
-    : T extends Promise<any>
-      ? ValidateSerializablePromise<T, TSerializable>
-      : T extends ReadableStream<any>
-        ? ValidateReadableStream<T, TSerializable>
-        : T extends Set<any>
-          ? ValidateSerializableSet<T, TSerializable>
-          : T extends Map<any, any>
-            ? ValidateSerializableMap<T, TSerializable>
-            : {
-                [K in keyof T]: ValidateSerializable<T[K], TSerializable>
-              }
+  : T extends ReadonlyArray<any>
+    ? ValidateSerializableArray<T, TSerializable>
+    : T extends (...args: Array<any>) => any
+      ? 'Function is not serializable'
+      : T extends Promise<any>
+        ? ValidateSerializablePromise<T, TSerializable>
+        : T extends ReadableStream<any>
+          ? ValidateReadableStream<T, TSerializable>
+          : T extends Set<any>
+            ? ValidateSerializableSet<T, TSerializable>
+            : T extends Map<any, any>
+              ? ValidateSerializableMap<T, TSerializable>
+              : {
+                  [K in keyof T]: ValidateSerializable<T[K], TSerializable>
+                }
 
 export type ValidateSerializablePromise<T, TSerializable> =
   T extends Promise<infer TAwaited>
@@ -69,6 +71,19 @@ export type ValidateSerializableMap<T, TSerializable> =
       >
     : never
 
+type ValidateSerializableArray<T extends ReadonlyArray<any>, TSerializable> =
+  IsTuple<T> extends true
+    ? { [K in keyof T]: ValidateSerializable<T[K], TSerializable> }
+    : T extends Array<infer U>
+      ? Array<ValidateSerializable<U, TSerializable>>
+      : ReadonlyArray<ValidateSerializable<T[number], TSerializable>>
+
+type IsTuple<T extends ReadonlyArray<any>> = T extends readonly []
+  ? true
+  : T extends readonly [any, ...infer _Rest]
+    ? true
+    : false
+
 export type RegisteredReadableStream =
   unknown extends SerializerExtensions['ReadableStream']
     ? never
@@ -175,11 +190,13 @@ export type ValidateSerializableInputResult<TRegister, T> =
 export type ValidateSerializableResult<T, TSerializable> =
   T extends TSerializable
     ? T
-    : unknown extends SerializerExtensions['ReadableStream']
-      ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
-      : T extends SerializerExtensions['ReadableStream']
-        ? ReadableStream
-        : { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+    : T extends ReadonlyArray<any>
+      ? ValidateSerializableArray<T, TSerializable>
+      : unknown extends SerializerExtensions['ReadableStream']
+        ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+        : T extends SerializerExtensions['ReadableStream']
+          ? ReadableStream
+          : { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
 
 export type RegisteredSSROption<TRegister> =
   unknown extends RegisteredConfigType<TRegister, 'defaultSsr'>
diff --git a/packages/router-core/tests/serializer-recursion.test-d.ts b/packages/router-core/tests/serializer-recursion.test-d.ts
new file mode 100644
index 0000000000..dbeb4b03bb
--- /dev/null
+++ b/packages/router-core/tests/serializer-recursion.test-d.ts
@@ -0,0 +1,15 @@
+import { describe, expectTypeOf, it } from 'vitest'
+
+import type {
+  Serializable,
+  ValidateSerializableResult,
+} from '../src/ssr/serializer/transformer'
+
+describe('ValidateSerializableResult recursion', () => {
+  it('should preserve recursive payload without infinite expansion', () => {
+    type Result = Array<Result> | { [key: string]: Result }
+    expectTypeOf<
+      ValidateSerializableResult<Result, Serializable>
+    >().branded.toEqualTypeOf<Result>()
+  })
+})

From 4fb6bb051af900a42681af1a00c88905d9d98b84 Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 03:31:36 +0100
Subject: [PATCH 02/14] fix: restore result array recursion

---
 .../router-core/src/ssr/serializer/transformer.ts     | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index 206fae1cec..68c62b61ee 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -191,13 +191,22 @@ export type ValidateSerializableResult<T, TSerializable> =
   T extends TSerializable
     ? T
     : T extends ReadonlyArray<any>
-      ? ValidateSerializableArray<T, TSerializable>
+      ? ValidateSerializableResultArray<T, TSerializable>
       : unknown extends SerializerExtensions['ReadableStream']
         ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
         : T extends SerializerExtensions['ReadableStream']
           ? ReadableStream
           : { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
 
+type ValidateSerializableResultArray<
+  T extends ReadonlyArray<any>,
+  TSerializable,
+> = IsTuple<T> extends true
+  ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+  : T extends Array<infer U>
+    ? Array<ValidateSerializableResult<U, TSerializable>>
+    : ReadonlyArray<ValidateSerializableResult<T[number], TSerializable>>
+
 export type RegisteredSSROption<TRegister> =
   unknown extends RegisteredConfigType<TRegister, 'defaultSsr'>
     ? SSROption

From 6d88b6f87c866b696f73072b354ca9e450a86bd0 Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 11:08:36 +0100
Subject: [PATCH 03/14] fix: distribute serializer validation over unions

---
 .../src/ssr/serializer/transformer.ts         | 55 ++++++++++---------
 .../tests/serializer-recursion.test-d.ts      | 19 +++++++
 2 files changed, 48 insertions(+), 26 deletions(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index 68c62b61ee..822ac42880 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -30,23 +30,24 @@ export interface CreateSerializationAdapterOptions<TInput, TOutput> {
   fromSerializable: (value: TOutput) => TInput
 }
 
-export type ValidateSerializable<T, TSerializable> = T extends TSerializable
-  ? T
-  : T extends ReadonlyArray<any>
-    ? ValidateSerializableArray<T, TSerializable>
-    : T extends (...args: Array<any>) => any
-      ? 'Function is not serializable'
-      : T extends Promise<any>
-        ? ValidateSerializablePromise<T, TSerializable>
-        : T extends ReadableStream<any>
-          ? ValidateReadableStream<T, TSerializable>
-          : T extends Set<any>
-            ? ValidateSerializableSet<T, TSerializable>
-            : T extends Map<any, any>
-              ? ValidateSerializableMap<T, TSerializable>
-              : {
-                  [K in keyof T]: ValidateSerializable<T[K], TSerializable>
-                }
+export type ValidateSerializable<T, TSerializable> =
+  T extends unknown
+    ? T extends TSerializable
+      ? T
+      : T extends ReadonlyArray<any>
+        ? ValidateSerializableArray<T, TSerializable>
+        : T extends (...args: Array<any>) => any
+          ? 'Function is not serializable'
+          : T extends Promise<any>
+            ? ValidateSerializablePromise<T, TSerializable>
+            : T extends ReadableStream<any>
+              ? ValidateReadableStream<T, TSerializable>
+              : T extends Set<any>
+                ? ValidateSerializableSet<T, TSerializable>
+                : T extends Map<any, any>
+                  ? ValidateSerializableMap<T, TSerializable>
+                  : { [K in keyof T]: ValidateSerializable<T[K], TSerializable> }
+    : never
 
 export type ValidateSerializablePromise<T, TSerializable> =
   T extends Promise<infer TAwaited>
@@ -188,15 +189,17 @@ export type ValidateSerializableInputResult<TRegister, T> =
   ValidateSerializableResult<T, RegisteredSerializableInput<TRegister>>
 
 export type ValidateSerializableResult<T, TSerializable> =
-  T extends TSerializable
-    ? T
-    : T extends ReadonlyArray<any>
-      ? ValidateSerializableResultArray<T, TSerializable>
-      : unknown extends SerializerExtensions['ReadableStream']
-        ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
-        : T extends SerializerExtensions['ReadableStream']
-          ? ReadableStream
-          : { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+  T extends unknown
+    ? T extends TSerializable
+      ? T
+      : T extends ReadonlyArray<any>
+        ? ValidateSerializableResultArray<T, TSerializable>
+        : unknown extends SerializerExtensions['ReadableStream']
+          ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+          : T extends SerializerExtensions['ReadableStream']
+            ? ReadableStream
+            : { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+    : never
 
 type ValidateSerializableResultArray<
   T extends ReadonlyArray<any>,
diff --git a/packages/router-core/tests/serializer-recursion.test-d.ts b/packages/router-core/tests/serializer-recursion.test-d.ts
index dbeb4b03bb..1e6e936a46 100644
--- a/packages/router-core/tests/serializer-recursion.test-d.ts
+++ b/packages/router-core/tests/serializer-recursion.test-d.ts
@@ -12,4 +12,23 @@ describe('ValidateSerializableResult recursion', () => {
       ValidateSerializableResult<Result, Serializable>
     >().branded.toEqualTypeOf<Result>()
   })
+
+  it('should preserve recursive tuples without infinite expansion', () => {
+    type ResultTuple = readonly [
+      ReadonlyArray<ResultTuple>,
+      { [key: string]: ResultTuple }
+    ]
+    expectTypeOf<
+      ValidateSerializableResult<ResultTuple, Serializable>
+    >().branded.toEqualTypeOf<ResultTuple>()
+  })
+
+  it('should preserve readonly recursive arrays without infinite expansion', () => {
+    type ResultReadonlyArray = ReadonlyArray<
+      ResultReadonlyArray | { [key: string]: ResultReadonlyArray }
+    >
+    expectTypeOf<
+      ValidateSerializableResult<ResultReadonlyArray, Serializable>
+    >().branded.toEqualTypeOf<ResultReadonlyArray>()
+  })
 })

From 72de9f34940a7590a20a470095767a5621477bc3 Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 12:30:13 +0100
Subject: [PATCH 04/14] more test cases and tiny type format tweaks

---
 .../src/ssr/serializer/transformer.ts         | 69 +++++++++----------
 .../tests/serializer-recursion.test-d.ts      | 26 ++++++-
 2 files changed, 58 insertions(+), 37 deletions(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index 822ac42880..aff1f873ea 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -30,24 +30,23 @@ export interface CreateSerializationAdapterOptions<TInput, TOutput> {
   fromSerializable: (value: TOutput) => TInput
 }
 
-export type ValidateSerializable<T, TSerializable> =
-  T extends unknown
-    ? T extends TSerializable
-      ? T
-      : T extends ReadonlyArray<any>
-        ? ValidateSerializableArray<T, TSerializable>
-        : T extends (...args: Array<any>) => any
-          ? 'Function is not serializable'
-          : T extends Promise<any>
-            ? ValidateSerializablePromise<T, TSerializable>
-            : T extends ReadableStream<any>
-              ? ValidateReadableStream<T, TSerializable>
-              : T extends Set<any>
-                ? ValidateSerializableSet<T, TSerializable>
-                : T extends Map<any, any>
-                  ? ValidateSerializableMap<T, TSerializable>
-                  : { [K in keyof T]: ValidateSerializable<T[K], TSerializable> }
-    : never
+export type ValidateSerializable<T, TSerializable> = T extends unknown
+  ? T extends TSerializable
+    ? T
+    : T extends ReadonlyArray<any>
+      ? ValidateSerializableArray<T, TSerializable>
+      : T extends (...args: Array<any>) => any
+        ? 'Function is not serializable'
+        : T extends Promise<any>
+          ? ValidateSerializablePromise<T, TSerializable>
+          : T extends ReadableStream<any>
+            ? ValidateReadableStream<T, TSerializable>
+            : T extends Set<any>
+              ? ValidateSerializableSet<T, TSerializable>
+              : T extends Map<any, any>
+                ? ValidateSerializableMap<T, TSerializable>
+                : { [K in keyof T]: ValidateSerializable<T[K], TSerializable> }
+  : never
 
 export type ValidateSerializablePromise<T, TSerializable> =
   T extends Promise<infer TAwaited>
@@ -188,27 +187,27 @@ export type RegisteredSerializationAdapters<TRegister> = RegisteredConfigType<
 export type ValidateSerializableInputResult<TRegister, T> =
   ValidateSerializableResult<T, RegisteredSerializableInput<TRegister>>
 
-export type ValidateSerializableResult<T, TSerializable> =
-  T extends unknown
-    ? T extends TSerializable
-      ? T
-      : T extends ReadonlyArray<any>
-        ? ValidateSerializableResultArray<T, TSerializable>
-        : unknown extends SerializerExtensions['ReadableStream']
-          ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
-          : T extends SerializerExtensions['ReadableStream']
-            ? ReadableStream
-            : { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
-    : never
+export type ValidateSerializableResult<T, TSerializable> = T extends unknown
+  ? T extends TSerializable
+    ? T
+    : T extends ReadonlyArray<any>
+      ? ValidateSerializableResultArray<T, TSerializable>
+      : unknown extends SerializerExtensions['ReadableStream']
+        ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+        : T extends SerializerExtensions['ReadableStream']
+          ? ReadableStream
+          : { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+  : never
 
 type ValidateSerializableResultArray<
   T extends ReadonlyArray<any>,
   TSerializable,
-> = IsTuple<T> extends true
-  ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
-  : T extends Array<infer U>
-    ? Array<ValidateSerializableResult<U, TSerializable>>
-    : ReadonlyArray<ValidateSerializableResult<T[number], TSerializable>>
+> =
+  IsTuple<T> extends true
+    ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+    : T extends Array<infer U>
+      ? Array<ValidateSerializableResult<U, TSerializable>>
+      : ReadonlyArray<ValidateSerializableResult<T[number], TSerializable>>
 
 export type RegisteredSSROption<TRegister> =
   unknown extends RegisteredConfigType<TRegister, 'defaultSsr'>
diff --git a/packages/router-core/tests/serializer-recursion.test-d.ts b/packages/router-core/tests/serializer-recursion.test-d.ts
index 1e6e936a46..063feff469 100644
--- a/packages/router-core/tests/serializer-recursion.test-d.ts
+++ b/packages/router-core/tests/serializer-recursion.test-d.ts
@@ -2,10 +2,32 @@ import { describe, expectTypeOf, it } from 'vitest'
 
 import type {
   Serializable,
+  ValidateSerializable,
   ValidateSerializableResult,
 } from '../src/ssr/serializer/transformer'
 
-describe('ValidateSerializableResult recursion', () => {
+describe('ValidateSerializable array handling', () => {
+  it('preserves nested array payloads for input validation', () => {
+    type Input = Array<{ value: string; nested: Array<{ id: number }> }>
+    expectTypeOf<
+      ValidateSerializable<Input, Serializable>
+    >().branded.toEqualTypeOf<Input>()
+  })
+
+  it('preserves tuple structure for input validation', () => {
+    type InputTuple = readonly [{ name: string }, { count: number }]
+    expectTypeOf<
+      ValidateSerializable<InputTuple, Serializable>
+    >().branded.toEqualTypeOf<InputTuple>()
+  })
+
+  it('preserves readonly array structure for input validation', () => {
+    type InputReadonlyArray = ReadonlyArray<{ value: string }>
+    expectTypeOf<
+      ValidateSerializable<InputReadonlyArray, Serializable>
+    >().branded.toEqualTypeOf<InputReadonlyArray>()
+  })
+
   it('should preserve recursive payload without infinite expansion', () => {
     type Result = Array<Result> | { [key: string]: Result }
     expectTypeOf<
@@ -16,7 +38,7 @@ describe('ValidateSerializableResult recursion', () => {
   it('should preserve recursive tuples without infinite expansion', () => {
     type ResultTuple = readonly [
       ReadonlyArray<ResultTuple>,
-      { [key: string]: ResultTuple }
+      { [key: string]: ResultTuple },
     ]
     expectTypeOf<
       ValidateSerializableResult<ResultTuple, Serializable>

From 4b65c4a8adc85587be408041d41bc21b07d2acca Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 12:38:58 +0100
Subject: [PATCH 05/14] ok i mean it's deduplicated but needs a leaf sentinel
 so whatevs

---
 .../src/ssr/serializer/transformer.ts         | 32 +++++++++++++------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index aff1f873ea..c8a4b1d1c3 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -71,12 +71,29 @@ export type ValidateSerializableMap<T, TSerializable> =
       >
     : never
 
-type ValidateSerializableArray<T extends ReadonlyArray<any>, TSerializable> =
+type ApplyArrayValidation<
+  TValue,
+  TSerializable,
+  TKind extends 'input' | 'result',
+> = TKind extends 'input'
+  ? ValidateSerializable<TValue, TSerializable>
+  : ValidateSerializableResult<TValue, TSerializable>
+
+type ValidateSerializableArrayCore<
+  T extends ReadonlyArray<any>,
+  TSerializable,
+  TKind extends 'input' | 'result',
+> =
   IsTuple<T> extends true
-    ? { [K in keyof T]: ValidateSerializable<T[K], TSerializable> }
+    ? { [K in keyof T]: ApplyArrayValidation<T[K], TSerializable, TKind> }
     : T extends Array<infer U>
-      ? Array<ValidateSerializable<U, TSerializable>>
-      : ReadonlyArray<ValidateSerializable<T[number], TSerializable>>
+      ? Array<ApplyArrayValidation<U, TSerializable, TKind>>
+      : ReadonlyArray<ApplyArrayValidation<T[number], TSerializable, TKind>>
+
+type ValidateSerializableArray<
+  T extends ReadonlyArray<any>,
+  TSerializable,
+> = ValidateSerializableArrayCore<T, TSerializable, 'input'>
 
 type IsTuple<T extends ReadonlyArray<any>> = T extends readonly []
   ? true
@@ -202,12 +219,7 @@ export type ValidateSerializableResult<T, TSerializable> = T extends unknown
 type ValidateSerializableResultArray<
   T extends ReadonlyArray<any>,
   TSerializable,
-> =
-  IsTuple<T> extends true
-    ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
-    : T extends Array<infer U>
-      ? Array<ValidateSerializableResult<U, TSerializable>>
-      : ReadonlyArray<ValidateSerializableResult<T[number], TSerializable>>
+> = ValidateSerializableArrayCore<T, TSerializable, 'result'>
 
 export type RegisteredSSROption<TRegister> =
   unknown extends RegisteredConfigType<TRegister, 'defaultSsr'>

From fe19e00bcff8eb8f8af55db83e0c20e7eca3a501 Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 12:51:18 +0100
Subject: [PATCH 06/14] use unknown instead of any

---
 .../router-core/src/ssr/serializer/transformer.ts  | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index c8a4b1d1c3..4e960df548 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -33,7 +33,7 @@ export interface CreateSerializationAdapterOptions<TInput, TOutput> {
 export type ValidateSerializable<T, TSerializable> = T extends unknown
   ? T extends TSerializable
     ? T
-    : T extends ReadonlyArray<any>
+    : T extends ReadonlyArray<unknown>
       ? ValidateSerializableArray<T, TSerializable>
       : T extends (...args: Array<any>) => any
         ? 'Function is not serializable'
@@ -80,7 +80,7 @@ type ApplyArrayValidation<
   : ValidateSerializableResult<TValue, TSerializable>
 
 type ValidateSerializableArrayCore<
-  T extends ReadonlyArray<any>,
+  T extends ReadonlyArray<unknown>,
   TSerializable,
   TKind extends 'input' | 'result',
 > =
@@ -91,13 +91,13 @@ type ValidateSerializableArrayCore<
       : ReadonlyArray<ApplyArrayValidation<T[number], TSerializable, TKind>>
 
 type ValidateSerializableArray<
-  T extends ReadonlyArray<any>,
+  T extends ReadonlyArray<unknown>,
   TSerializable,
 > = ValidateSerializableArrayCore<T, TSerializable, 'input'>
 
-type IsTuple<T extends ReadonlyArray<any>> = T extends readonly []
+type IsTuple<T extends ReadonlyArray<unknown>> = T extends readonly []
   ? true
-  : T extends readonly [any, ...infer _Rest]
+  : T extends readonly [unknown, ...Array<unknown>]
     ? true
     : false
 
@@ -207,7 +207,7 @@ export type ValidateSerializableInputResult<TRegister, T> =
 export type ValidateSerializableResult<T, TSerializable> = T extends unknown
   ? T extends TSerializable
     ? T
-    : T extends ReadonlyArray<any>
+    : T extends ReadonlyArray<unknown>
       ? ValidateSerializableResultArray<T, TSerializable>
       : unknown extends SerializerExtensions['ReadableStream']
         ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
@@ -217,7 +217,7 @@ export type ValidateSerializableResult<T, TSerializable> = T extends unknown
   : never
 
 type ValidateSerializableResultArray<
-  T extends ReadonlyArray<any>,
+  T extends ReadonlyArray<unknown>,
   TSerializable,
 > = ValidateSerializableArrayCore<T, TSerializable, 'result'>
 

From 2c14a2c982273c77473b8c7ad3db647155c727a3 Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 13:03:52 +0100
Subject: [PATCH 07/14] remove now unused IsTuple type

---
 .../src/ssr/serializer/transformer.ts         | 31 ++++++++-----------
 1 file changed, 13 insertions(+), 18 deletions(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index 4e960df548..6df279c7f3 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -31,10 +31,10 @@ export interface CreateSerializationAdapterOptions<TInput, TOutput> {
 }
 
 export type ValidateSerializable<T, TSerializable> = T extends unknown
-  ? T extends TSerializable
-    ? T
-    : T extends ReadonlyArray<unknown>
-      ? ValidateSerializableArray<T, TSerializable>
+  ? T extends ReadonlyArray<unknown>
+    ? ValidateSerializableArray<T, TSerializable>
+    : T extends TSerializable
+      ? T
       : T extends (...args: Array<any>) => any
         ? 'Function is not serializable'
         : T extends Promise<any>
@@ -83,24 +83,19 @@ type ValidateSerializableArrayCore<
   T extends ReadonlyArray<unknown>,
   TSerializable,
   TKind extends 'input' | 'result',
-> =
-  IsTuple<T> extends true
-    ? { [K in keyof T]: ApplyArrayValidation<T[K], TSerializable, TKind> }
-    : T extends Array<infer U>
+> = T extends any
+  ? number extends T['length']
+    ? T extends Array<infer U>
       ? Array<ApplyArrayValidation<U, TSerializable, TKind>>
       : ReadonlyArray<ApplyArrayValidation<T[number], TSerializable, TKind>>
+    : { [K in keyof T]: ApplyArrayValidation<T[K], TSerializable, TKind> }
+  : never
 
 type ValidateSerializableArray<
   T extends ReadonlyArray<unknown>,
   TSerializable,
 > = ValidateSerializableArrayCore<T, TSerializable, 'input'>
 
-type IsTuple<T extends ReadonlyArray<unknown>> = T extends readonly []
-  ? true
-  : T extends readonly [unknown, ...Array<unknown>]
-    ? true
-    : false
-
 export type RegisteredReadableStream =
   unknown extends SerializerExtensions['ReadableStream']
     ? never
@@ -205,10 +200,10 @@ export type ValidateSerializableInputResult<TRegister, T> =
   ValidateSerializableResult<T, RegisteredSerializableInput<TRegister>>
 
 export type ValidateSerializableResult<T, TSerializable> = T extends unknown
-  ? T extends TSerializable
-    ? T
-    : T extends ReadonlyArray<unknown>
-      ? ValidateSerializableResultArray<T, TSerializable>
+  ? T extends ReadonlyArray<unknown>
+    ? ValidateSerializableResultArray<T, TSerializable>
+    : T extends TSerializable
+      ? T
       : unknown extends SerializerExtensions['ReadableStream']
         ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
         : T extends SerializerExtensions['ReadableStream']

From 4fd2e248650f3445972439d4c08ff09d263a4c72 Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 13:40:45 +0100
Subject: [PATCH 08/14] retain variadic tuple fidelity in the types

---
 .../src/ssr/serializer/transformer.ts         | 28 +++++++++++++------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index 6df279c7f3..65dd7009a5 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -79,16 +79,24 @@ type ApplyArrayValidation<
   ? ValidateSerializable<TValue, TSerializable>
   : ValidateSerializableResult<TValue, TSerializable>
 
+type IsTuple<T extends ReadonlyArray<unknown>> = T extends readonly []
+  ? true
+  : T extends readonly [unknown, ...infer TRest]
+    ? TRest extends ReadonlyArray<unknown>
+      ? true
+      : false
+    : false
+
 type ValidateSerializableArrayCore<
   T extends ReadonlyArray<unknown>,
   TSerializable,
   TKind extends 'input' | 'result',
 > = T extends any
-  ? number extends T['length']
-    ? T extends Array<infer U>
+  ? IsTuple<T> extends true
+    ? { [K in keyof T]: ApplyArrayValidation<T[K], TSerializable, TKind> }
+    : T extends Array<infer U>
       ? Array<ApplyArrayValidation<U, TSerializable, TKind>>
       : ReadonlyArray<ApplyArrayValidation<T[number], TSerializable, TKind>>
-    : { [K in keyof T]: ApplyArrayValidation<T[K], TSerializable, TKind> }
   : never
 
 type ValidateSerializableArray<
@@ -204,11 +212,15 @@ export type ValidateSerializableResult<T, TSerializable> = T extends unknown
     ? ValidateSerializableResultArray<T, TSerializable>
     : T extends TSerializable
       ? T
-      : unknown extends SerializerExtensions['ReadableStream']
-        ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
-        : T extends SerializerExtensions['ReadableStream']
-          ? ReadableStream
-          : { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+      : T extends (...args: Array<any>) => any
+        ? 'Function is not serializable'
+        : unknown extends SerializerExtensions['ReadableStream']
+          ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+          : T extends SerializerExtensions['ReadableStream']
+            ? ReadableStream
+            : {
+                [K in keyof T]: ValidateSerializableResult<T[K], TSerializable>
+              }
   : never
 
 type ValidateSerializableResultArray<

From c92e23c5cd064568feab11c198c3b6a5c6ca439a Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 14:03:42 +0100
Subject: [PATCH 09/14] test cov for Promise and ReadableStream recursive
 containers

---
 .../tests/serializer-recursion.test-d.ts      | 24 +++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/packages/router-core/tests/serializer-recursion.test-d.ts b/packages/router-core/tests/serializer-recursion.test-d.ts
index 063feff469..4df82d5b73 100644
--- a/packages/router-core/tests/serializer-recursion.test-d.ts
+++ b/packages/router-core/tests/serializer-recursion.test-d.ts
@@ -28,6 +28,30 @@ describe('ValidateSerializable array handling', () => {
     >().branded.toEqualTypeOf<InputReadonlyArray>()
   })
 
+  it('preserves recursive payloads wrapped in Promise for input validation', () => {
+    type Recursive = { value: number; next?: Recursive }
+    type InputPromise = Promise<Recursive>
+    expectTypeOf<
+      ValidateSerializable<InputPromise, Serializable>
+    >().branded.toEqualTypeOf<InputPromise>()
+  })
+
+  it('preserves recursive payloads wrapped in Promise<Array> for input validation', () => {
+    type Recursive = { value: number; children?: Array<Recursive> }
+    type InputPromiseArray = Promise<Array<Recursive>>
+    expectTypeOf<
+      ValidateSerializable<InputPromiseArray, Serializable>
+    >().branded.toEqualTypeOf<InputPromiseArray>()
+  })
+
+  it('preserves recursive payloads wrapped in ReadableStream for input validation', () => {
+    type Recursive = { value: number; next?: Recursive }
+    type InputStream = ReadableStream<Recursive>
+    expectTypeOf<
+      ValidateSerializable<InputStream, Serializable>
+    >().branded.toEqualTypeOf<InputStream>()
+  })
+
   it('should preserve recursive payload without infinite expansion', () => {
     type Result = Array<Result> | { [key: string]: Result }
     expectTypeOf<

From 3c5f2cf2d816e749ec4a4affeba05b7e0566a1de Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 16:15:04 +0100
Subject: [PATCH 10/14] use more efficient tuple test

---
 packages/router-core/src/ssr/serializer/transformer.ts | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index 65dd7009a5..15541bee55 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -79,13 +79,9 @@ type ApplyArrayValidation<
   ? ValidateSerializable<TValue, TSerializable>
   : ValidateSerializableResult<TValue, TSerializable>
 
-type IsTuple<T extends ReadonlyArray<unknown>> = T extends readonly []
-  ? true
-  : T extends readonly [unknown, ...infer TRest]
-    ? TRest extends ReadonlyArray<unknown>
-      ? true
-      : false
-    : false
+type IsTuple<T extends ReadonlyArray<unknown>> = number extends T['length']
+  ? false
+  : true
 
 type ValidateSerializableArrayCore<
   T extends ReadonlyArray<unknown>,

From 0bbb80087d9b7e4721bbe662865b16d267ff825e Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 16:15:29 +0100
Subject: [PATCH 11/14] get rid of separate IsTuple helper just do the check
 inline

---
 packages/router-core/src/ssr/serializer/transformer.ts | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index 15541bee55..4574809388 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -79,20 +79,16 @@ type ApplyArrayValidation<
   ? ValidateSerializable<TValue, TSerializable>
   : ValidateSerializableResult<TValue, TSerializable>
 
-type IsTuple<T extends ReadonlyArray<unknown>> = number extends T['length']
-  ? false
-  : true
-
 type ValidateSerializableArrayCore<
   T extends ReadonlyArray<unknown>,
   TSerializable,
   TKind extends 'input' | 'result',
 > = T extends any
-  ? IsTuple<T> extends true
-    ? { [K in keyof T]: ApplyArrayValidation<T[K], TSerializable, TKind> }
-    : T extends Array<infer U>
+  ? number extends T['length']
+    ? T extends Array<infer U>
       ? Array<ApplyArrayValidation<U, TSerializable, TKind>>
       : ReadonlyArray<ApplyArrayValidation<T[number], TSerializable, TKind>>
+    : { [K in keyof T]: ApplyArrayValidation<T[K], TSerializable, TKind> }
   : never
 
 type ValidateSerializableArray<

From b94486cabcf55233e056c1750bfdbd1b35bd865d Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 20:53:37 +0100
Subject: [PATCH 12/14] we gotta treat tuples differently i guess

---
 .../src/ssr/serializer/transformer.ts         | 82 +++++++++++--------
 1 file changed, 46 insertions(+), 36 deletions(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index 4574809388..bba2b3f667 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -30,8 +30,8 @@ export interface CreateSerializationAdapterOptions<TInput, TOutput> {
   fromSerializable: (value: TOutput) => TInput
 }
 
-export type ValidateSerializable<T, TSerializable> = T extends unknown
-  ? T extends ReadonlyArray<unknown>
+export type ValidateSerializable<T, TSerializable> =
+  T extends ReadonlyArray<unknown>
     ? ValidateSerializableArray<T, TSerializable>
     : T extends TSerializable
       ? T
@@ -45,8 +45,9 @@ export type ValidateSerializable<T, TSerializable> = T extends unknown
               ? ValidateSerializableSet<T, TSerializable>
               : T extends Map<any, any>
                 ? ValidateSerializableMap<T, TSerializable>
-                : { [K in keyof T]: ValidateSerializable<T[K], TSerializable> }
-  : never
+                : {
+                    [K in keyof T]: ValidateSerializable<T[K], TSerializable>
+                  }
 
 export type ValidateSerializablePromise<T, TSerializable> =
   T extends Promise<infer TAwaited>
@@ -71,30 +72,27 @@ export type ValidateSerializableMap<T, TSerializable> =
       >
     : never
 
-type ApplyArrayValidation<
-  TValue,
-  TSerializable,
-  TKind extends 'input' | 'result',
-> = TKind extends 'input'
-  ? ValidateSerializable<TValue, TSerializable>
-  : ValidateSerializableResult<TValue, TSerializable>
-
-type ValidateSerializableArrayCore<
+type ValidateSerializableArray<
   T extends ReadonlyArray<unknown>,
   TSerializable,
-  TKind extends 'input' | 'result',
-> = T extends any
-  ? number extends T['length']
-    ? T extends Array<infer U>
-      ? Array<ApplyArrayValidation<U, TSerializable, TKind>>
-      : ReadonlyArray<ApplyArrayValidation<T[number], TSerializable, TKind>>
-    : { [K in keyof T]: ApplyArrayValidation<T[K], TSerializable, TKind> }
-  : never
+> = number extends T['length']
+  ? T extends Array<infer U>
+    ? Array<ValidateSerializable<U, TSerializable>>
+    : ReadonlyArray<ValidateSerializable<T[number], TSerializable>>
+  : ValidateSerializableTuple<T, TSerializable>
 
-type ValidateSerializableArray<
+type ValidateSerializableTuple<
   T extends ReadonlyArray<unknown>,
   TSerializable,
-> = ValidateSerializableArrayCore<T, TSerializable, 'input'>
+> = T extends readonly [infer THead, ...infer TTail]
+  ? readonly [
+      ValidateSerializable<THead, TSerializable>,
+      ...ValidateSerializableTuple<
+        TTail extends ReadonlyArray<unknown> ? TTail : [],
+        TSerializable
+      >,
+    ]
+  : T
 
 export type RegisteredReadableStream =
   unknown extends SerializerExtensions['ReadableStream']
@@ -199,26 +197,38 @@ export type RegisteredSerializationAdapters<TRegister> = RegisteredConfigType<
 export type ValidateSerializableInputResult<TRegister, T> =
   ValidateSerializableResult<T, RegisteredSerializableInput<TRegister>>
 
-export type ValidateSerializableResult<T, TSerializable> = T extends unknown
-  ? T extends ReadonlyArray<unknown>
+export type ValidateSerializableResult<T, TSerializable> =
+  T extends ReadonlyArray<unknown>
     ? ValidateSerializableResultArray<T, TSerializable>
     : T extends TSerializable
       ? T
-      : T extends (...args: Array<any>) => any
-        ? 'Function is not serializable'
-        : unknown extends SerializerExtensions['ReadableStream']
-          ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
-          : T extends SerializerExtensions['ReadableStream']
-            ? ReadableStream
-            : {
-                [K in keyof T]: ValidateSerializableResult<T[K], TSerializable>
-              }
-  : never
+      : unknown extends SerializerExtensions['ReadableStream']
+        ? { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
+        : T extends SerializerExtensions['ReadableStream']
+          ? ReadableStream
+          : { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
 
 type ValidateSerializableResultArray<
   T extends ReadonlyArray<unknown>,
   TSerializable,
-> = ValidateSerializableArrayCore<T, TSerializable, 'result'>
+> = number extends T['length']
+  ? T extends Array<infer U>
+    ? Array<ValidateSerializableResult<U, TSerializable>>
+    : ReadonlyArray<ValidateSerializableResult<T[number], TSerializable>>
+  : ValidateSerializableResultTuple<T, TSerializable>
+
+type ValidateSerializableResultTuple<
+  T extends ReadonlyArray<unknown>,
+  TSerializable,
+> = T extends readonly [infer THead, ...infer TTail]
+  ? readonly [
+      ValidateSerializableResult<THead, TSerializable>,
+      ...ValidateSerializableResultTuple<
+        TTail extends ReadonlyArray<unknown> ? TTail : [],
+        TSerializable
+      >,
+    ]
+  : T
 
 export type RegisteredSSROption<TRegister> =
   unknown extends RegisteredConfigType<TRegister, 'defaultSsr'>

From c0d048aab3c47e66cf04e7fa1b5808bfa0878eae Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 22:22:06 +0100
Subject: [PATCH 13/14] i sure hope an abstraction doesn't break things again

---
 .../src/ssr/serializer/transformer.ts         | 85 ++++++++-----------
 1 file changed, 36 insertions(+), 49 deletions(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index bba2b3f667..0a55aed499 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -32,7 +32,7 @@ export interface CreateSerializationAdapterOptions<TInput, TOutput> {
 
 export type ValidateSerializable<T, TSerializable> =
   T extends ReadonlyArray<unknown>
-    ? ValidateSerializableArray<T, TSerializable>
+    ? ResolveArrayShape<T, TSerializable, 'input'>
     : T extends TSerializable
       ? T
       : T extends (...args: Array<any>) => any
@@ -45,9 +45,7 @@ export type ValidateSerializable<T, TSerializable> =
               ? ValidateSerializableSet<T, TSerializable>
               : T extends Map<any, any>
                 ? ValidateSerializableMap<T, TSerializable>
-                : {
-                    [K in keyof T]: ValidateSerializable<T[K], TSerializable>
-                  }
+                : { [K in keyof T]: ValidateSerializable<T[K], TSerializable> }
 
 export type ValidateSerializablePromise<T, TSerializable> =
   T extends Promise<infer TAwaited>
@@ -72,28 +70,6 @@ export type ValidateSerializableMap<T, TSerializable> =
       >
     : never
 
-type ValidateSerializableArray<
-  T extends ReadonlyArray<unknown>,
-  TSerializable,
-> = number extends T['length']
-  ? T extends Array<infer U>
-    ? Array<ValidateSerializable<U, TSerializable>>
-    : ReadonlyArray<ValidateSerializable<T[number], TSerializable>>
-  : ValidateSerializableTuple<T, TSerializable>
-
-type ValidateSerializableTuple<
-  T extends ReadonlyArray<unknown>,
-  TSerializable,
-> = T extends readonly [infer THead, ...infer TTail]
-  ? readonly [
-      ValidateSerializable<THead, TSerializable>,
-      ...ValidateSerializableTuple<
-        TTail extends ReadonlyArray<unknown> ? TTail : [],
-        TSerializable
-      >,
-    ]
-  : T
-
 export type RegisteredReadableStream =
   unknown extends SerializerExtensions['ReadableStream']
     ? never
@@ -199,7 +175,7 @@ export type ValidateSerializableInputResult<TRegister, T> =
 
 export type ValidateSerializableResult<T, TSerializable> =
   T extends ReadonlyArray<unknown>
-    ? ValidateSerializableResultArray<T, TSerializable>
+    ? ResolveArrayShape<T, TSerializable, 'result'>
     : T extends TSerializable
       ? T
       : unknown extends SerializerExtensions['ReadableStream']
@@ -208,28 +184,6 @@ export type ValidateSerializableResult<T, TSerializable> =
           ? ReadableStream
           : { [K in keyof T]: ValidateSerializableResult<T[K], TSerializable> }
 
-type ValidateSerializableResultArray<
-  T extends ReadonlyArray<unknown>,
-  TSerializable,
-> = number extends T['length']
-  ? T extends Array<infer U>
-    ? Array<ValidateSerializableResult<U, TSerializable>>
-    : ReadonlyArray<ValidateSerializableResult<T[number], TSerializable>>
-  : ValidateSerializableResultTuple<T, TSerializable>
-
-type ValidateSerializableResultTuple<
-  T extends ReadonlyArray<unknown>,
-  TSerializable,
-> = T extends readonly [infer THead, ...infer TTail]
-  ? readonly [
-      ValidateSerializableResult<THead, TSerializable>,
-      ...ValidateSerializableResultTuple<
-        TTail extends ReadonlyArray<unknown> ? TTail : [],
-        TSerializable
-      >,
-    ]
-  : T
-
 export type RegisteredSSROption<TRegister> =
   unknown extends RegisteredConfigType<TRegister, 'defaultSsr'>
     ? SSROption
@@ -262,3 +216,36 @@ export type ValidateSerializableLifecycleResultSSR<
     : RegisteredSSROption<TRegister> extends false
       ? any
       : ValidateSerializableInput<TRegister, LooseReturnType<TFn>>
+
+type ResolveArrayShape<
+  T extends ReadonlyArray<unknown>,
+  TSerializable,
+  TMode extends 'input' | 'result',
+> = number extends T['length']
+  ? T extends Array<infer U>
+    ? Array<ResolveArrayElement<U, TSerializable, TMode>>
+    : ReadonlyArray<ResolveArrayElement<T[number], TSerializable, TMode>>
+  : ResolveTupleShape<T, TSerializable, TMode>
+
+type ResolveTupleShape<
+  T extends ReadonlyArray<unknown>,
+  TSerializable,
+  TMode extends 'input' | 'result',
+> = T extends readonly [infer THead, ...infer TTail]
+  ? readonly [
+      ResolveArrayElement<THead, TSerializable, TMode>,
+      ...ResolveTupleShape<
+        TTail extends ReadonlyArray<unknown> ? TTail : [],
+        TSerializable,
+        TMode
+      >,
+    ]
+  : T
+
+type ResolveArrayElement<
+  TValue,
+  TSerializable,
+  TMode extends 'input' | 'result',
+> = TMode extends 'input'
+  ? ValidateSerializable<TValue, TSerializable>
+  : ValidateSerializableResult<TValue, TSerializable>

From 7b18dc8ce998526518329690ceb48d63a0df6099 Mon Sep 17 00:00:00 2001
From: Brooke Holmes <git@brooke.me>
Date: Wed, 24 Sep 2025 22:52:54 +0100
Subject: [PATCH 14/14] wip

---
 .../src/ssr/serializer/transformer.ts            | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index 0a55aed499..564800811f 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -223,8 +223,8 @@ type ResolveArrayShape<
   TMode extends 'input' | 'result',
 > = number extends T['length']
   ? T extends Array<infer U>
-    ? Array<ResolveArrayElement<U, TSerializable, TMode>>
-    : ReadonlyArray<ResolveArrayElement<T[number], TSerializable, TMode>>
+    ? Array<ArrayModeResult<TMode, U, TSerializable>>
+    : ReadonlyArray<ArrayModeResult<TMode, T[number], TSerializable>>
   : ResolveTupleShape<T, TSerializable, TMode>
 
 type ResolveTupleShape<
@@ -233,19 +233,15 @@ type ResolveTupleShape<
   TMode extends 'input' | 'result',
 > = T extends readonly [infer THead, ...infer TTail]
   ? readonly [
-      ResolveArrayElement<THead, TSerializable, TMode>,
-      ...ResolveTupleShape<
-        TTail extends ReadonlyArray<unknown> ? TTail : [],
-        TSerializable,
-        TMode
-      >,
+      ArrayModeResult<TMode, THead, TSerializable>,
+      ...ResolveTupleShape<Readonly<TTail>, TSerializable, TMode>,
     ]
   : T
 
-type ResolveArrayElement<
+type ArrayModeResult<
+  TMode extends 'input' | 'result',
   TValue,
   TSerializable,
-  TMode extends 'input' | 'result',
 > = TMode extends 'input'
   ? ValidateSerializable<TValue, TSerializable>
   : ValidateSerializableResult<TValue, TSerializable>